This invention generally relates to a flexure assembly that is useful for guiding motion of components in devices such as vibration test equipment.
A variety of vibration test devices are commercially available and commonly referred to as shakers or exciters or vibration generators. There are several basic components within most such devices including an armature suspended for movement relative to a stator. A coil is typically carried by the armature and located in an air gap between the armature and the stator. Permanent magnets are electromagnets are typically used to generate a D.C. magnetic field across the air gap. By feeding an alternating current through the coil, the armature is caused to reciprocate or vibrate along its longitudinal axis relative to the stator at the frequency of the applied alternating current.
Since the armature must move relative to the stator, it is typically mounted with a series of bearings and/or a plurality of peripheral suspension members. The bearings and suspension members serve the functions of centering the armature and allowing it to move along its longitudinal axis. Preferably, the armature is prevented from any lateral movement normal to the longitudinal axis along which the armature moves during vibration. A variety of bearings and suspension members have been proposed in the past, however, none have proven satisfactory for all conditions and circumstances. Typical problems with existing arrangements include distortion of the purity of the vibration motion caused by typical suspension members. Additionally, conventional arrangements typically do not adequately restrict off-axis movement and do not provide the degree of accuracy that is needed in many situations. Moreover, none of the prior systems adequately address all of these issues.
An additional problem presented by conventional bearings and suspension members is that they typically introduce noise during the vibration movement. Any additional noise is undesirable under circumstances where the purpose of the vibratory test is to determine squeaks and rattles within an item that is being tested. One example includes instrument panels that are included in passenger vehicles. During a testing operation, the ability to detect squeaks and rattles within an assembled instrument panel is compromised by extraneous noises that are created by the bearings or suspension members within the testing device.
Therefore, there is a need for an improved assembly that will allow for an armature within a vibration testing device to move along its longitudinal axis while also preventing any cross-axis motion and doing so with minimal noise. This invention addresses those needs and overcomes the shortcomings and drawbacks of the prior art described above.
Another type of motion that is often needed for testing is rotary or pivotal motion. Conventional arrangements do not adequately accommodate such motion. Hinge or bearing arrangements typically do not limit off-axis motion sufficiently. Additionally, friction and noise typically are concerns and cause problems.
Additional problems are presented when shakers are used in a laboratory setting or any manufacturing facility for performing product validation and squeak and rattle testing for complete automotive vehicles, for example. Typically, simulated road conditions are input to the vehicle through the tire patch and chassis suspension. Typical equipment arrangements induce large displacements (up to 4 inches) and large forces (up to 10,000 pounds). To achieve these results, hydraulic actuators are typically used.
There are many shortcomings and drawbacks with conventional road simulators used as squeak and rattle testing devices. Most arrangements create high noise levels that mask the existence, and impede the identification of squeaks and rattles in the vehicle interior. The noise of the testing equipment makes it difficult to distinguish between squeak and rattle noises within the vehicle and those caused by the testing equipment. It is most important to minimize or eliminate ambient test equipment noises. Otherwise, the technicians are left with a subjective assessment that requires them to separate and discriminate the test equipment noises from actual vehicle squeak and rattle noises. This renders objective measurements difficult, uncorrelated and typically unreliable.
Another shortcoming associated with conventional arrangements is that the maximum frequency for inducing motion of the vehicle is typically limited to approximately 100 Hz. These limitations are usually associated with performance limitations of hydraulic actuators. For example, hydraulic arrangements can seldom achieve higher frequencies, but even if they do, the relatively high pressure oil arrangements are sometimes considered a safety or environmental concern. Squeaks and rattles within a vehicle are typically identified at higher frequencies in the range from about 300 to 500 Hz. Conventional arrangements are often not capable of exciting at these higher frequencies thus restricting a technician from identifying possible sources of undesirable noise.
Another shortcoming with conventional road simulating test equipment is that it is typically very expensive to purchase and install. Large masses or foundations are typically needed to react the large forces introduced by the test equipment, which complicates and increases the expense of the installation. Additionally, hydraulic power supplies are expensive to operate and maintain and are associated with high power consumption and other environmental issues.
Utilizing the innovations of this invention, avoids the drawbacks and shortcomings of prior arrangements. This invention provides the possibility for testing for squeaks and rattles within a vehicle unlike what has been achieved in the past.
In general terms, this invention is a flexure assembly that is useful for supporting and guiding components in a testing assembly that repeatedly moves an object in a chosen direction. A device designed according to this invention is particularly useful for testing squeak and rattle noises in a vehicle. The inventive device includes a vibration source that has a moving portion that moves reciprocally along a vibration axis. A plurality of flexure assemblies permit movement of the moving portion along the vibration axis and restrict movement of the moving portion in other directions. A transition member is adapted to directly engage the vehicle body structure to transmit motion of the moving portion to the vehicle body structure.
In a preferred embodiment, the transition member has a first end adapted to engage the vehicle body structure and a second end that is adapted to engage the moving portion of the vibration source. A midportion of the transition member has a pivot axis about which the transition member pivots responsive to movement of the moving portion of the vibration source. The inventive arrangement also preferably includes a noiseless flexure pivot assembly at the pivot axis that permits the transition member to pivot about the pivot axis without making any audible noise.
In the preferred arrangement, the flexure pivot assembly includes at least two pivot members that each permits movement in one direction but resist movement in other directions. The pivot members are positioned relative to each other such that the transition member is permitted to pivot about the pivot axis, but is restrained from moving in other directions. The ends of the pivot members preferably remain fixed relative to each other at each end of the assembly. The flexure pivot assembly of this invention provides a noiseless arrangement, which is especially useful for detecting squeaks and rattles in a vehicle.